The present invention relates to a composite for forming an electrode of an ignition plug (a spark plug).
An ignition plug (a spark plug) has been used for ignition of a device (e.g. an internal combustion engine) to burn fuel. As the ignition plug, a plug having electrodes (e.g. a center electrode and a ground electrode) forming a discharge gap is used. As such electrodes, an electrode formed by a composite having a first member and a second member that is joined to the first member could be used. For instance, the center electrode is formed by a composite having a rod-shaped metal member and a tip made of noble metal etc. and joined to an end portion of the metal member. And, the ground electrode has a rod-shaped metal member and a tip joined to an end portion of the metal member, and the tip of this ground electrode is formed by a composite having a supporting member made of alloy etc. having nickel and a tip made of noble metal etc. and joined to the supporting member. To form a proper electrode, it is preferable that when two members of the composite are joined, a relative position of the two members be a proper position. As a technique of joining the two members at a proper position, for instance, International Publication WO2012039381 discloses that a first tip is held by a chuck, an eccentric error of a center axis of the first tip is detected by image processing, and when the eccentric error falls outside a tolerance range, a position of the first tip is corrected, then a second tip is laser-welded to this position-corrected first tip.